Orchard heating system &amp; burner

ABSTRACT

A system for supplying liquefied petroleum or gaseous fuel to an array of grove heaters including a central gas supply valving distribution system and thermostatic control. The system includes a number of high efficiency heaters, each with a shielded pilot flame burner and assembly and automatic cutoff valve in the event of pilot flame extinguishment. The burner includes a helical flame path in intimate contact with a tubular body member constituting horizontal radiating surface and a top diffuser cover for optimum heat distribution in a horizontal direction. The burner assembly includes a shielded pilot flame with a continuous metal flame attachment member for insuring the expansion of burner flame from pilot to full flame in full operation without flameout. The burner includes a temperature responsive valve which is effective and readily adjustable in the field.

United States Patent 1 1 v [111 3,825,183 Machlanski July 23, 1974 ORCHARD HEATING SYSTEM & BURNER Primary Examiner--William E. Wayner [76] Inventor: Sigmund H. Machlanski, 7017 Park Attorney Agent or Flrm Jhn Wagner Lawn Dr., Gregory, Mich. 48137 [22] Filed: Dec. 13, 1972 ABSTRACT [21] Appl No.; 314,631 A system for supplying liquefied petroleum or gaseous fuel to an array of grove heaters including a central Related Apphcatlon Data gas supply valving distribution system and thermol Division Of 125,053, March 17, 1971, static control. The system includes a number of high Io-317501642- efflciency heaters, each with a shielded pilot flame burner and assembly and automatic cutoff valve in the [52] US. Cl 236/93, 236/8, 236/103 event of pilot fl extinguishment The burner [51] Int. Cl. GOSd 23/275 cludes a helical flame path in i i Contact i a [58] Fleld of Search 236/1021 93? tubular body member constituting horizontal radiating 239/569 surface and a top diffuser cover for optimum heat distribution in a horizontal direction. The burner assem- [56] References cued bly includes a shielded pilot flame with a continuous UNITED STATES PATENTS metal flame attachment member for insuring the exss1,3ss 4/1907 Stuart 236/102 Pansion 0f burner flame from pilot to full flame in full 1,062,639 5/1913 Dixon 236/103 operation without flameout. The burner includes a 1,960,343 V 5/1934 236/103 temperatureresponsive valve which is effective and 2,653,454 9/1953 Buchel 236/102 UX r adily adjustable in th field, 3,199,834 8/1965 Short 236/102 X 6 Claims, 14 Drawing Figures PATENTEUJULZBIHH SHEET 3 BF 4 iii 1 ORCHARD HEATING SYSTEM & BURNER This is a division of my co-pending application Ser. No. 125,053 filed on Mar. 17, 1971 now US. Pat. No. 3,750,642.

BACKGROUND OF THE INVENTION The primary source of grove heating of citrus, avocadosand related cold sensitive trees and plants has been the free standing stack burner which is normally placed between rows of frost-sensitive trees. Whenever frost danger becomes imminent, the heaters are charged with oil and lit. Constant monitoring, refueling, relighting of extinguished burners and extinguishing burners at the end of frost danger requires a large use of manpower in an extremely short period of time, particularly when lighting of the burners is necessitated. The conventional burner, although inexpensive to manufacture and to operate, is inefficient as a burner and much heat is generated and is ineffectively used. The burners produce significant amounts of unburned combustion products tending to pollute the atmosphere.

A more recent development in the area of frost protection is the use of airborne helicopters which, on an emergency basis, can hover over a grove and maintain a constant flow of air in and about the trees because of the natural downdraft of the helicopter rotor blades. Each of the foregoing systems have advantages, for example, the oil burner is traditionally considered low in cost in operation and manufacture, but high in labor cost. Wind machines, each of which can cover a large number of trees, can be started remotely and are found to require less labor at the time. It has been found, however, that the engines are not reliable and require significant maintenance and a failure to start can mean a large loss to the grower. Furthermore, under certain conditions of extreme cold without a warmer inversion layer overhead, use of wind machines worsens situation.

Orchard heaters employing fuel supplied from a common storage tank to a number of spaced heaters is known in the art as represented by US. Pat. Nos. 3,451,387 and 3,391,683.

BRIEF STATEMENT OF THE INVENTION In order to satisfy the need for unmanned operation to gas fired heaters in applications such as grove heating, and to do this in a satisfactory manner, requires the achievement of a number of objectives simultaneously. It is necessary that a reliable means of automatic ignition be provided. It is desirable that the heater have built-in safety features to cutoff discharge of raw gas in the event of flameout. From the ecological point of view, it is desirable that the heater burn its fuel in a manner which minimizes the discharge of combustion products classified as pollutants. These include oxides of nitrogen, carbon monoxide and unburned hydrocarbons. For open areas, it is desirable that the heater provide heat transfer by radiation to the surroundings in preference to strictly conduction and convection. It is essential that the heater operate whenfully exposed to the weather--wind, rain and icing conditions. The subject invention'achieves all of these objectives in an apparatus of extreme simplicity.

With the foregoing state of the prior art, I have invented a new orchard heating system employing a central'storage tank, thermostatic control, pressure regulator and a distribution system of piping to a number of spaced heaters preferably under trees to be protected. Each burner includes an upstanding metal tube constituting the body of the burner with means for securing it to the ground, such as stakes. An internal helical path between the bottom of the burner tube and the upper outlet is defined by a helical internal baffle. A burner head assembly is positioned in the lower portion of the burner body, directing the flame into the helical path.

I prevent opening of the gas feed line to the main burner unless a pilot flame is sensed. In many cases, a similar but separate means is employed to cutoff the pilot burner supply in the event of flameout, requiring a manual override before the system can be relighted. In the subject invention, all of these functions are combined in a single unit containing an integral heat sensing element/cutoff valve.

In another embodiment of this invention, the valve burner head includes a tubular shroud which comminicates with a flat disc-like orifice structure wherein the normal pilot flame rests on the orifice protected from extinguishment by the shroud. In both of the burner and valve assemblies, the similar temperature responsive valve stem extends rearwardly out of the valve assembly and is maintained in place by a frictional engagement with a locking device whereby adjustments may be made merely by light tapping applied to the rear of the valve stem.

BRIEF DESCRIPTION OF THE DRAWINGS The above features of this invention may be more clearly understood by the following detailed description and by reference to the drawings in which:

FIG. 1 is a schematic drawing of the system in accordance with this invention;

FIG. 2 is an enlarged perspective view of a single burner of the system of FIG. 1;

FIG. 3 is an elevational view with portions broken away for clarity of the burner head and valve assembly in accordance with this invention;

FIG. 4 is an elevational view of the heater of this invention with portions broken away for clarity;

FIG. 5 is a side elevational ,view of the multi-stage burner assembly of this invention with portions broken away for clarity;

FIG. 6 is a top view of the assembly of FIG. 5;

FIG. 7 is a side view partly in section of an alternate embodiment of a valve and burner head of this invention;

FIG. 8A is a plan view of the blank used in forming preferred form of pilot flame shroud in accordance with this invention;

FIGS. 88 and C are side elevational and end views, respectively, of the shroud of FIGS. 5 and 6;

FIGS. 9A, B and C are simplified longitudinal views of the burner assembly of this invention showing various stages of flame development; and,

FIG. 10 is a fragmentary perspective view of an alternate form of helical flame conduit for the burner of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION Now referring to FIG. 1, a system of this invention showing a typical installation includes a storage tank for liquefied petroleum located adjacent to the orchard to be protected. The storage tank, particularly for use of propane, butane or comparable fuels, includes a fuel delivery system including valve 11, solenoid valve 12 and main delivery pipe 13. The solenoid valve 12 is under control of one or more thermostats 14 located in a critical area for detection of early frosting conditions. The delivery pipe 13 communicates with a main distribution line 15, for example, of l inch diameter piping from which a number of branch lines or laterals 20 extend into the orchard or area to be protected. Each of the laterals 20 has a number of burners 21 denoted in the drawing by hexagonal symbols. The burners 21 are located either under individual trees in the orchard or between trees at intervals dictated by the heating capacity of the burner and requirements in a particular grove.

The gas supply system, in addition to the main feed supply to the burner 21, includes a pilot supply including line 22, shut-off valve 23, and pressure regulator 24 communicating to the main line 13 at T-joint 25.Each of the burners 21 have automatic cut-off in the event of pilot failure completing the fully automatic supply system of this invention.

Now referring to FIG. 2, the basic configuration of each burner 21 of FIG. 1 may be seen. The burner is basically an upstanding metal tube 26 supported on the plurality of metal stakes 30 which may be driven into the ground for support. The bottom and the top of the tube 26 are opened with the top opening in the form of an annular region between the upper end of the tube 26 and a rain and wind shield 31. This shield 31 is supported by a number of integral depending legs 32 secured to the tube 26 side wall. The supply tube 33 for fuel enters the burner 21 at the bottom of tube 26. The details of the internal construction and its novel features are shown more clearly in FIG. 4 described below.

Now referring to FIG. 4, the portion of the side wall 26 is broken away to show the internal heating tube details of the burner. The internal components of the burner 21 include basically the fuel feed 33 which supplies liquid fuel to the side of the burner assembly 40 via a preheating loop 41 and an inlet 42 at the rear of a valve burner head 43. The preheating loop 44 constitutes an extension of fuel feedline 33 and is positioned beside the third stage 45 of the burner assembly. The preheating loop 44 is joined to the feedline 33 by a second loop 46 which is designed to give a bit of flexibility in the positioning of the preheating unit 44. Thus, the preheating unit 44 and the third stage 45 can be adjusted merely by bending the feedline. Also, where tight coupling and a high degree of preheating is desired, the preheating loop 44 may be placed under clip 47 and then be in direct metal-to-metal contact with the third stage 45. It is in the preheating loop 44 that liquid fuel arriving over line 33 is vaporized without any pressure reducing valve or other mechanical device which might become faulty.

It should be noted in FIG. 4 that the burner assembly is positioned with the basic bum'er head 43 adjacent to a side wall 26. In the immediate region at the base of burner 43 is a lighting opening 48 through which a torch is inserted for lighting purposes. With the torch directed at the opening 48, the flame passes beside or envelopes the burner head 43 heating the'internal valve and extends toward the nozzle area to immediately ignite gas issuing from the nozzle. In other words, the lighting of the burner is achieved from the rear rather than the front with the intended danger of blowout of a feeble flame encountered in some other types of burners.

The burner assembly of the heater includes-the valve and burner head 43 which extends into a first stage enclosure 44 which in turn communicates with a third stage enclosure 45. The burner assembly of the heater ,is secured to a flat helix 50 which extends from the lower region of the body 26 to the top of the heater. The helix 50 is maintained in its stretched position by a pair of rods 51 and 52 extending between opposed openings in the wall of the tube 26. Each of the rods 51 and 52 engages curve end lip 55, one of which appears in the drawing. The edges of the helix 50 are in nominal contact with the inner wall of the tube 26 but contact is not mandatory. The helix 50 defines a helix combustion gas path up through the burner in the region of the side wall whereby the side wall is maintained in radiant heating condition and whereby the exhaust gases are emitted radially from the annular port 38 between the tubular 26 and cover 31.

Thus, it may be seen from FIG. 4 that the sheet metal tube 26 encasing the helix 50 forms the outer wall of the combustion chamber. There is no inner wall closing this chamber since centrifugal action of the gases keeps the flow hugging the outer wall.

The key element of the heater is the burner which incorporates the functions of pilot flame holder, main burner nozzle and temperature responsive cutoff valve in a single five piece assembly illustrated in the FIG. 3. The valve and burner head 43 constituting the heart of this invention is disclosed in half-section in FIG. 3, to which reference is now made. It includes basically an elongated body 60 threaded at each end and tapered to a knife edge at the rear end in the region 61. The rear end in the region of the taper 61 includes lock nut 62 engaging the threads of the body 60. The front or nozzle end of the valve and burner head 43 similarly is enclosed by a lock nut 63 open at the end including two pair of cross-diametrical slots 64, one of which appears in the drawing. The lock nut 63 holds a valve block 65 in position on the end of the body 60. The valve block includes frusto conical recess 66 which joins a tubular portion 67 closed except for orifice 70. Flow to the orifice between the feedline 33 and inlet 22 in the orifice 70 is controlled by valve stem 71 having a tapered point 72 mating with the frusto conical valve seat portion 66 of the valve block 65. The valve stem 71 is held in position against the valve seat 66 by the lock nut 62 at the opposite end. The nut 62 having an internal tapered surface 73 compresses the tapered portion 61 of valve body 60 against the side wall of the valve stem 71. The valve stem 71 as seen in the drawing extends out of the valve body and lock nut 62 where its end is exposed.

Of prime importance is the fact that the valve body 60 and the valve stem 71 are of materials having a significantly different thermal coefficients of expansion with the valve body having the larger coefficient. Preferred material are brass for the valve body 60 and INVAR for the valve stem 71. Valve body 60 has a thermal coefficient of expansion in the order of X l0 in/in/F and has an overall length of approximately 2 inches while the valve stem 71 has a negligible coefficient of expansion.

Although the relative motion between stem 71 and block 65 for a typical design case is measured in thousandths of an inch for temperature changes measured in hundreds of degrees, the motion is adequate from a practical point of view. With the valve seat diameter 66 being large relative to the diameter of the control orifice 70 (as described previously), less than two thousands of an inch lift from shut-off position will increase the flow area through the valve to the point where the fixed control orifice 70 becomes the critical flow controlling area (which is the desired result). This will occur in the case of the configuration described and illustrated with a temperature increase of 100F. Practical operating temperatures of the burner assembly are in the 500 to 1,000F range so it is clear thatthere is ample margin for positive actuation from fully closed to fully open in the temperature range from ambient (around 75F) to burner operating at rated output (burner nozzle at around 750F). Although the valve lift is minute, the opening and closing forces available are very large. The force available to break any valve stiction or interference to motion is determined by the compressive spring force represented by the solid valve stem 71 and valve body 60. The spring rate in compression of these solid parts is readily made sufficiently high to assure positive operation of the valve under adverse circumstances. This, it is pointed out, is an additional feature of the valve assembly. Dirt or particulate matter is the bane of satisfactory valve operation, as a general rule. In the applications under consideratiomthe presence of dirt or particulates is also a particular hazard to the proper operation of the small control orifice used to regulate the gasflow rate. Plugging of such orifices is a common problem and when it occurs, generally requires disassembly to clear the obstruction. In operation with gaseous hydrocarbon fuels such as propane, there is always the possibility of premature breakdown of the fuel and formation of carbonaceous deposits and particles in the burner entry passages.

The invention described provides a filter or dirt trap upstream of the control orifice which tends to clear itself each cycle of operation. (A cycle is defined either as proceeding from shut-off to full operation and return to shut-off, or from pilot flame operation to rated operation and back to pilot level).

The annular gap at the valve seat 66 varies from zero to a few thousandths inch in width (shut-off to rated operation). Downstream of this annular gap is the control orifice 70 with a diameter on the order of 0.025 inches. It is obvious, therefore, that particles of carbon accumulations will be blocked at the annular gap presented by the valve opening unless they are small enough to pass freely through the control orifice. These accumulations, particularly the carbonaceous type particles, tend to be crushed by the valve when it seats itself or when the gap closes under the reduced operating temperature associated with pilot operation. Subsequent return to full open allows the crushed particles to wash through the much larger control orifice. We see, therefore, that the described invention incorporates a self-cleaning filter or trap action.

The pilot flame is supported by the cross-slotted tip of the burner nozzle 63 which provides the characteristics of a flame holder and primary stage air injector. At the extremely low operating pressures used to sustain pilot flames (less tahn Va psig), the pilot flame will assume a wafer shape trapped within and held securely by the flame holding action of the cross-slotted nozzle tip. The single point injection orifice in the valve block 65 is the only gas feed in the burner covering the full range of operation from pilot to rated operation.

In a typical case of a rated 60,000 BTU/hr. heater, this represents an operating range on the order of 300 to 1. This single point injection is an essential feature of the invention since the valve block 65 is required to perform two functions in itself. The first is the fixed control orifice regulating the flow rate of the gas as a function of pressure. This calibrated control orifice is simply a carefully sized central hole 70 in the valve block 65. The second function provided by the valve block 65 is provision of the valve seat 66 for the cut-off valve. The self-actuating cut-off valve consists of .a valve stem 71 of finite length (in a typical design about '2 inches long) secured at one end to the valve body 60 and the free end is guided into a port which has a diameter which is large relative to the control orifice diameter downstream. (In a working model, the ratio of 8/1 in diameters has proven effective.) In the figure shown, a conical valve stem tip is shown engaging the lip of the valve seat. This is but one of avariety of valve pintle and seat configurations which may be employed. The exact configuration is not significant to the invention. The valve actuation takes place in response to temperature changes since the valve stern is made of a material (such as INVAR) which has a very low thermal coefficient of expansionwhile the valve body is made of a material (such as brass) with a relatively high coefficient of expansion. It may be seen,therefore, that from an operating position with the valve open, a reduction in temperature of these parts will cause the valve body to shrink relative to the valve stem. The valve stem and valve body are securely locked together at one end while the other end of the valve body has the valve block clamped in place. As a result, the valve stem face (at the free end of the valve stem) moves toward the valve seat (in the valve block) with decreasing temperatures. When properly set, the valve will close fully at ambient temperatures in the normal range (below l00F) and will open when heated to higher temperatures.

The valve stem 71 is secured to the valve body 60 by means of the locking action created by the drawing down of the lock nut 62 on a tapered section 61 of the valve body 60. The lock nut 62 has a correspondingly tapered or curved contour which wedges the tapered lip 61 of the valve body 60 securely against the valve stem 71. This action not only locks the stem in position, but also provides a gas seal at this end of the assembly.

The assembly and setting of the valve is extremely simple. Initially, the valve seat 66 in the valve body 65 is simply a sharp edge, as machined. The assembly is lightly tightened at room temperature and then the exposed end of the valve stem 71 is driven down until a seat is coined in the valve block 65 by the valve stem 71 itself. This seat matches the valve taper 72 exactly as a result. A source of gas pressure can be applied during this process to make a simultaneous leak check varifying proper seating of the valve. When properly seated, the valve assembly is torqued full tight and secured. No further calibration operations are required. It will be found that applying heat to the assembly will result in the valve opening as expected.

Now referring to FIG. which is an elevational view of the burner assembly, including the valve burner head 43 contained within a rectangular housing 40 with a portion of the valve body 60 and lock nut 62 extending out of the housing 40 a sufficient distance that the fuel inlet 42 is exposed. The rear end 80 of the valve stem 71 also is exposed facilitating seating an adjustment as described above in connection with FIG. 3. The valve and burner head 43 are secured to the housing 40 by a spring clip 91.

Encircling and in frictional engagement with the front lock nut 63 is a tubular shroud 92 having an integral inner helical extension 93 which originates adjacent to the burner orifice thereby presenting a metal edge for the pilot flame to attach as it expands outward. The open end of shroud 92 communicates with the second stage chamber 94 of the burner defined by the sheet metal rectangular housing 45 which in turn includes a pair of vanes 96, one of which appears in the drawing defining a third expansion chamber 97. This valve and burner head 93 secured horizontally within the chamber 40 in position to assure that there is a smooth transition from initial pilot flame through the helix 93 through the open end of shroud 92, through chamber 94 and chamber 97 with a minimum of danger of discontinuity or loss of flame upon expansion. The chamber 97 communicates with the helical path shown in FIG. 4 defined by the helix 50 of FIG. 4 whereby the gases leaving the burner are introduced into the helical chamber bounded by the outer surface 26 of the burner housing as shown in FIG. 4.

The physical arrangement of the valve and burner head 40 and chambers is further illustrated in top view of FIG. 6. In this Fig., the arrangement for mounting the entire burner assembly upon the helical support plate 50 includes four machine screws 101 ,and wing flanges 102 and 103 of the burner assembly. The burner assembly as shown in FIG. 6 includes air inlet regions designated in the drawing by the letters A, B and C. The openings A, B and C are proportioned directly to the air requirements for efficient flame generation in burning at each expansion stage.

Proceeding further with description of the heater, the design features of the successive burner stages will be discussed with specific reference to the features incorporated to perform the desired multiple functions in a unique manner. It will be recalled that the total range of operation can be made very large with the subject device. Operating a self-aspirating burner with a single injector over such a broad range requires the use of multiple stages with provision for smooth transfer from one stage to the next (to preclude blowout).

This is accomplished in the successive stages illustrated in the FIGS. 5 and 6. The valve burner head 43 has already been described as constituting stage one of the burner progression. The second stage is the formed sheet metal outer tube 92 with a doubled internal helical. The entire piece housing 40, 45 is formed from a single piece of flat sheet stock. The inner tube 92 rests on the outer diameter of the burner nozzle 63 of the burner head assembly. The close geometric relationship between this tubular section 92 and the slotted nozzle 63 maintains a small step for the expanding flame to bridge. This design feature promotes smooth transition. Further, as the flame velocity is increased and the flame front advances accordingly, it finds the helical edge 93 of the inner tube 92 leading it out to the full diameter of the outer tube 92. The flame is stabilized by attachment to such edges and surfaces.

The tubular second stage 92 is attached to the third stage by metal clips or tabs unshown in the drawing in such a manner that the continued expansion of the flame front is led from one contiguous surface to another assuring uninterrupted attachment of a portion of the advancing flame. The third stage is a tunnel shaped member 45 enshrouding the main portions of the first and second stages with a relatively close fitting section. This section guides the air being sucked in by aspiration along the axes of the burner and prevents cross currents from impinging on the pilot flame chamber. Close to the exit plane of the second stage, the third stage tunnel is shaped to provide an expansion section with air inlet flaps for a major admixture of additional inlet air, but guided for flow in only the outlet direction. This again restricts the path for reverse or cross gusts that could blow out the pilot flame during pilot standby operation. At each transition plane, the expansion is limited to an acceptably moderate step and provision is made for attachment of the advancing flame on a continuous basis from one contiguous surface to another.

It will be noted that these successive stages are overlapped to the rear in each case so that they present a labyrinth passageway with bypasses and deflectors which strongly attenuate any wayward gust of wind which might find its way to this portion of the heater during pilot operation and thus the pilot flame is provided with a series of successive protective barriers.

The entire assembly comprising the burner head and pilot stage 43, together with the second and third stages, is attached to the spiral sheet metal ramp 50, which forms the upper and lower walls of the helical fourth stage combustion chamber. The sheet metal stack or tube 26 encasing the spiral forms the outer wall of the combustion chamber.

The flame front advancing between the exit flaps 96 of the third stage is turned partially by these flaps which are curved to initiate the spinning mode of the fourth stage, best illustrated in FIG. 4. The contiguous surface at the plane of attachment between the spiral ramp 50 and the initial combustor stage assembly provides the continuity of attachment sought. The underside of the spiral ramp 50 (which is the ceiling) is the selected attachment surface since the convective forces drive the flame to the ceiling of the passageway.

Having entered the fourth stage combustor stack, the burning gas is deflected in a spinning mode along the helical trough as it forces its way upward to the exit gap between the outer wall and the top cover. The resultant vortex action has a number of desirable characteristics. The scrubbing action of the flame against the outer skin of the heater provides very effective heat transfer to this, the primary radiating wall. The vortex also eliminates the necessity for an inner wall and enables the use of the open center well as a central chimney drawing up copious quantities of heated air which is free to mix with the combustion process along the full length of the effective combustion chamber. All of the air is forced into mixing somewhere along the path since the only exit is across the full width of the combustion zone at the top opening. The heated air rising up the center well, freely being drawn into the vortexing combustion process along the way and forced by deflection at the top cover to cross the combustion zone before exiting at the rim, assures the presence of excess oxygento complete the combustion process. The design not only assures the presence of excess oxygen, but adequate stay time to complete the chemical process.

The achievement of combustion without ejection of pollutants requires understanding and control of the combustion process. The two factors which are of major importance in this regard are (l) combustion temperature (the production of nitrous oxides occurs most vigorously at peak combustion temperatures), and (2) incomplete combustion due to inadequate supply and mixing of air and/or inadequate stay time in a combustion zone. A blow torch type flame from an open gas burner head may appear to burn in a clean manner with a clear blue flame, but in actuality, a significant portion of the gaseous fuel has no time to complete the combustion process in the short transit from burner face to expansion into the atmosphere. As a result, the heating value is degraded and the atmosphere is polluted by the unburned gas.

My invention controls the combustion process to maintain a reduced peak temperature (minimizing nitrogen oxide generation) in a manner which can be adjusted by simple means; and also assures complete combustion by providing a surplus of preheated air along a lengthy combustion passage before the products are discharged.

Radiant heat transfer is a function of the temperature of the radiating body. Since it increases as the fourth power of the radiating body temperature (doubling the heater wall temperature increases the radiant energy output 16 fold), it is clear that operation of the heater at the highest possible temperature of the radiating surface is desirable. The subject invention is designed to concentrate the released chemical energy of the combustion process primarily in the sidewalls of the heater while keeping the top and bottom surfaces relatively cooler. By the nature of the design and its adjustability, the sidewalls can be operated close to the maximum temperature permissible for the wall material employed. In this way,-the greatest possible amount of heat is transferred by radiation, and in particular, transferred laterally to surrounding objects rather than to the sky or to the ground. For example, in a 60,000 BTU/hr design, the entire heater assembly is contained in a 10 inch diameter stack 26 with an enclosure length of one foot. Yet the combustion passage in which the combustion process is continuously maintained has an effective length of more than 5 feet.

The arrangement of the exit port, the center air well and the air inlet port also contribute to protection of the pilot flame. The inlet air port is a central hole in the bottom plate which is the same size as the air well formed within the spiral ramp 50. Cross gusts cannot enter this port directly since it is horizontal and close to the ground. Only deflected effects will be felt at this entry point. At the top, the exit gap presents a clear passage from one side to the other so wind gusts enter- Air enters the inlet port during normal burner operation drawn in by both the chimney effect of the central column of air (which is exposed to intense heating by radiation) and also by the aspirator characteristics designed into the successive burner stages. The initial burner stages are located in the spiral ramp at the completion of the first turn upward. The flow direction enforced by the configuration not only forces the combustion mixture into the spinning mode already described, but draws the primary mixing air in along the same path. In this manner, a spinning mode is imparted to this portion of the air as it approaches the burner (or initial stage). This air is preheated by the very hot surface over which it flows which contributes toward efficient combustion.

The air plenum chamber formed at the bottom, and the spreading air exiting outward along the top surface both act as buffer zones which reduce the temperature of the top and bottom surfaces to minimize radiation heat transfer to sky and ground. On the other hand, the concentration of the combustion process at the sidewalls maximizes the temperature and therefore the radiant heat transfer from this surface.

This temperature can be excessive both from the point of view of pollution due to nitrogen oxide formation and the ability of the wall material or structure to withstand operation at this temperature. Reduction of the peak operating temperature is adjustably controlled in the subject invention by mixing a discrete portion of the combustion products back into the primary air. The mixing of combustion products into the air reduces the amount of available oxygen in the mixture. The nitrogen in the air itself performs a similar function reducing the peak temperature of combustion when compared with combustion involving pure oxygen.

This is accomplished in the design by forming a vane arrangement shown in FIG. 10 through the simple device of slitting the spiral wall at an interface between combustion zone and air preheat chamber, as illustrated in FIG. 4 as region I. The slit portions are twisted to take the shape of diverting vanes and simultaneously open a passage between the two zones. By adjustment, the desired admixture is achieved. A direct measure of calibration is the color of the hottest wall section of the heater where the combustion temperature is at its peak. The use of slit vanes as illustrated in FIG. 10 is but one' of a variety of means which could be employed to cfing one side will tend to exit directly out the other side with minimum reflection down the stack. Any reflection that does occur will tend to dissipate itself down through the open center well and out the bottom port which is right in line.

fect the same result, that is, the mixture of a portion of the combustion products with the primary air to reduce the temperature of the hottest zone in the heater.

Although the burner assembly of FIG. 3 with its helical shroud as shown in FIGS. 5 and 6 is preferred, a different form of valve and burner assembly may also be used and such an embodiment is illustrated in FIG. 7. In FIG. 7, components which are identical to those of the valve and burner assembly of FIGS. 4 and 5 are given identical nominal designations. In this case, the body includes a gas inlet 42 and a rear lock nut 121 along with a front lock nut 122 which defines the first combustion chamber. A lock nut 121 holds a valve stem 71 which is identical with the same of FIGS. 3 and 5. Its end 80 extends out the rear of the assembly of FIG. 7. A valve block 123 cooperates with the valve stem 71 in the same manner as the valve block 65 of FIG. 3. This valve block 123 includes an orifice 124 which communicates with the first chamber 125 within the lock nut 122. Air for the pilot flame is supplied through a plurality of radial openings 126. The chamber 125 communicates with a frusto conical expansion area 130 which is closed by front baffle wall 131 in the outer or second stage shroud 132. This baffle wall 131 includes an orifice 133 through which a flame expands into the second stage area 134 within a shroud 132. Additional air for combustion in the region 134 is supplied through a plurality of radially located orifices 135 in the shroud 132.

The valve and burner head of FIG. 7 includes the same basic principle of automatic valve closing in the event of pilot failure in that the valve stem 71 is made of a metal having a thermal coefficient of expansion much less than that of the body 120 and it is positioned to provide the normal pilot flame gas flow through the orifice 124 when the assembly is in a heated condition by the burning pilot flame. Again, the body 120 is preferably brass and the valve stem 71 of INVAR. With the rear end 80 of pintle 71 exposed, adjustments in the opening may be accomplished by loosening lock nut 121 and tapping or withdrawing the end 80 as required. In the case of this burner head in FIG. 7 upon the application of full burning pressure to the system, the gas flow to the orifice 124 increases and the flame advances sequentially to the chambers 125 and 126, mi fices 133, and chamber 134 and, thence, into the expansion chambers 94 and 95 of the assembly of FIGS. and 6. As indicated above, the embodiment of FIG. 7 is shown as an alternate embodiment although not preferred inasmuch as it includes a number of additional and more complex parts to provide the same function as compared with the burner head of FIG. 3.

Now refer to FIG. 8 in which the shroud of the preferred embodiment of burner head may be seen. The shroud 92 as shown in FIG. 5 is made from a piece of sheet metal including a generally rectangular area 140 with a tapered extension 141. The shroud 92 is preferably of heat and corrosion resistant steel. The shroud is made by first rolling the tab portion 141 into a loose open tube with an internal diameter matching that of the nozzle of the burner head 43 and then the rectangular portion 140 is rolled typically in the opposite direction to provide an outer cylindrical tube. The configuration of the completed assembly appears in FIG. 88 as simply a tube 92 or the view from the end in FIG. 8C where the tube may be seen as including the outer tubular portion formed from the rectangular section 140 showing joining the inner counterwound helical portion 141. This shroud assembly, as simple as it is in design, is effective when merely snapped over the end of the nozzle assembly 43.

The relationship of the shroud 92 to the burner 43 is further illustrated in FIG. 9 which illustrates the stages of expansion of a flame from stage one or pilot operation in FIG. 9A with the flame attached to the shroud helix to stage two shown in FIG. 98 where the flame appears at the outlet of shroud 92, to stage three shown in FIG. 9C where the flame is in the chambers 94 and 95 from which it expands in stage four to the spiral chamber of the burner of FIG. 4.

All of these accomplishments are embodied in a system of utmost simplicity, as shown in the foregoing description. This reduces the manufacturing cost of the heater itself. In addition, by incorporating the preheating features enabling operation with cold, liquefied gas fed directly to the heater; field installations are made simpler and less costly. This results since the pipe size required to carry liquefied gas is much smaller than for the same mass flow rate of gas, and since no separate means need be provided to convert the liquefied gas to the gaseous state.

The above described embodiments of this invention are merely descriptive of its principles and are not to be considered limiting. The scope of this invention instead shall be determined from the scope of the following claims, including their equivalents.

What is claimed is:

l. A thermally responsive valve comprising:

a body including a tubular recess including a conical outlet orifice at one end of said recess and an inlet;

an elongated unitary valving member positioned within said recess including an end surface tapered to close said orifice when in contact therewith;

means securing said valving member to said body at a point remote from said orifice;

said body having a significantly greater coefficient of thermal expansion I than said valving member whereby flow through said orifice varies with temperature of said body and valving member wherein said body expands on increases in temperature to open an annular fluid passage between said conical outlet orifice and said tapered end surface; and

said valving member including a cylindrical portion extending out of said body and said means securing said valving member is adjustably secured to said body and in frictional and sealing engagement with said valving member whereby the seating of said valving member may be adjusted from the exterior of said valve by axial pressure applied to said valving member.

2. The combination in accordance with claim 1 wherein said valving member comprises a cylindrical rod with one end region tapered and cooperating with said valve seat to define said controlled orifice and the opposite end extends through a mating cylindrical opening in valve body in frictional contact therewith.

3. The combination in accordance with claim 1 wherein said valving member is Invar.

4. A thermally responsive valve comprising a tubular valve body having a pair of open end couplings in threaded engagement with opposite ends of said tubular valve body;

a valve block including an orifice therethrough and a valve seat portion aligned with the axis of said tubular valve body;

one of said open end couplings securing said valve block to said valve body and providing a discharge opening for said valve;

a valve stem member including one end engaging the valve seat portion of said valve block and extending through the center of said valve body; said valve body having a significantly greater coefficient of thermal expansion than said valve stem member while flow through said discharge opening varies with the temperature of said valve body and said valve stem member whereby said body expands on increase in temperature to open said orifice between said valve blocks and said valve stem member;

tween the exterior and interior of said valve body through said orifice.

5. The combination in accordance with claim 4 wherein the opening of said first open end coupling comprises a burner nozzle.

6. The combination in accordance with claim 4 wherein said first and second open end couplings are substantially identical. 

1. A thermally responsive valve comprising: a body including a tubular recess including a conical outlet orifice at one end of said recess and an inlet; an elongated unitary valving member positioned within said recess including an end surface tapered to close said orifice when in contact therewith; means securing said valving member to said body at a point remote from said orifice; said body having a significantly greater coefficient of thermal expansion than said valving member whereby flow through said orifice varies with temperature of said body and valving member wherein said body expands on increases in temperature to open an annular fluid passage between said conical outlet orifice and said tapered end surface; and said valving member including a cylindrical portion extending out of said body and said means securing said valving member is adjustably secured to said body and in frictional and sealing engagement with said valving member whereby the seating of said valving member may be adjusted from the exterior of said valve by axial pressure applied to said valving member.
 2. The combination in accordance with claim 1 wherein said valving member comprises a cylindrical rod with one end region tapered and cooperating with said valve seat to define said controlled orifice and the opposite end extends through a mating cylindrical opening in valve body in frictional contact therewith.
 3. The combination in accordance with claim 1 wherein said valving member is Invar.
 4. A thermally responsive valve comprising a tubular valve body having a pair of open end couplings in threaded engagement with opposite ends of said tubular valve body; a valve block including an orifice therethrough and a valve seat portion aligned with the axis of said tubular valve body; one of said open end couplings securing said valve block to said valve body and providing a discharge opening for said valve; a valve stem member including one end engaging the valve seat portion of said valve block and extending through the center of said valve body; said valve body having a significantly greater coefficient of thermal expansion than said valve stem member while flow through said discharge opening varies with the temperature of said valve body and said valve stem member whereby said body expands on increase in temperature to open said orifice between said valve blocks and said valve stem member; the second of said open end couplings securing said valve stem member to said valve body remote from said valve block; said valve stem member in frictional and sealing engagement and with the opening of said second open end coupling and extending out of said valve for adjustment by axial pressure applied to exposed portion of said valve stem member; and means defining a fluid passage communicating between the exterior and interior of said valve body through said orifice.
 5. The combination in accordance with claim 4 wherein the opening of said first open end coupling comprises a burner nozzle.
 6. The combination in accordance with claim 4 wherein said first and second open end couplings are substantially identical. 